Techniques of Removal of Dye Colour and Chemicals from Textile Effluents

 Techniques of Removal of Dye Colour and Chemicals from Textile Effluents

     

Aaditya Patel and Shahsikant Karwa | Textile chemistry and Textile technology, DKTE Society's Textile and Engineering Institute | August 28, 2020

Abstract

In study and research of effluent generation in textile industry. Textile wastewater includes a large variety of dyes and chemical which get remains in to the bath and create drainage. This has to be treated properly before releasing into nature. The majority of the waste water comes from the dyeing and finishing process. The chemical reagents used are diverse in chemical composition, ranging from inorganic compounds to polymers and organic products. In exhaust dyeing, which is in fact the most popular method, dye bath is not exhausted completely in most of the cases only sustainable exhaustion is achieve. This paper will enlighten the various methods/technique used for removal of color and other chemicals where as various facts and figures from textile effluent

Keywords

Waste water, toxic, oxygen demand, harmful factor, filters, harmful factors.

Introduction

Requirement of waste water treatment (effluent)

The waste water contains mutagenic, carcinogenic and toxic components. The presence of low concentration of dyes in effluent is highly visible and undesirable. This liquid contains high toxicity. Also the water consist of heavy metals that are complex compounds.

Pollutants in textile effluent are mainly of five different types based on.Their ease in bio-degradation:-

• Relatively harmless inorganic contaminants, viz. alkalis, mineral acids, neutral salts and oxidizing agents like peroxides, chlorine and chlorine dioxide.

• Moderate to high BOD but are readily degradable, viz. starch sizes, vegetable oils, fats and waxes, biodegradable surfactants, organic acids and reducing agents.

• Dyes and polymers difficult to biodegrade (too high BOD value with too slower degradation), viz. dyes and fluorescent brighteners, fibres and polymeric impurities, polyacrylate sizes, synthetic polymer finishes and silicones.

• Moderate BOD and difficult to biodegrade, viz, wool grease, PVA sizes, starch ethers and esters, mineral oil, surfactants, anionic and non-ionic softeners

• Negligible BOD but unsuitable for conventional biological treatment, viz. HCHO and N-methylol reactants, chlorinated solvents and carriers cationic retarding and softening agents, biocides, sequestering agents and heavy metal salts.

Table.1 The typical limits for discharge of effluent into public sewage.

Methods which can be applicable for removal of colors of dyes and other chemical from effluent. Methods are as follow:

The method has the ability to clarify, concentration and most importantly to separate dye continuously from the effluent.

Main five type of process based membrane:

1. Micro filtration

• Size-0.1-10 microns.

• Removes sand, silt, clay, giardia, lambia, cryptosporidium, cysts, algae, some bacterial species and oil emulsion.

• Used in the separation of oil and water emulsions

2. Ultra filtration

• The process is similar to reverse osmosis.

• Size-0.003-0.1 microns.

• Removes soluble organic materials, protozoa, bacteria, and viruses.

• Used as a pretreatment of nano filtration and reverse osmosis.

3. Nano filtration

• Size-0.001microns.

• Pressure-driven filtration process - 0.600 to 1000 kilopascal pressure is required.

• It removes micro molecular organic compounds

• Micro-organism, hardness of water, demineralization, colour removal.

• Used in desalination.

4. Reverse osmosis

• Size-0.001 microns.

• It removes natural organic substances, pesticides, cysts, bacteria, viruses.

• Used in desalination

5. Electro dialysis

• Membrane type is cation and anion exchange membrance.

• Membrane material is sulfonated cross-linked polystyrene.

• Process diving force is electrical potential gradient.

• It use to removes desalting of ionic solution.

Table.2 membrance processes based on pore size which derives prepare required Size filter membrance.

Whereas we has seen above method which has help for removal of colour by physical method. But still there are many more by which we get better results. This method are generally done by adsorption. Adsorption is the phenomenon by which the molecules of a gas, vapors or liquid spontaneously concentrate at contacting surface without undergoing any reaction. The use of an adsorbent, whether ion exchange, activated carbon or high surface area inorganic material, for removing species from liquid stream depends on the equilibrium between the adsorbed and free species

Adsorbent Activated carbon

• Activated carbon has been evaluated extensively for the treatment of different classes of dyes.

• The molecular structure of a dye has a significant effect on the extent to which it will be absorbed with decreasing solubility and polarity of the dye.

• Factors such as choice of activated carbon, temperature, pH, contact time and dosage must be taken into consideration for optimal removal of dyes from wastewater.

• Limitation it is highly costly and also 15-18% of loss due to reactivity of dye.

Waste of sugar cane (the remaining portion of sugarcane after removal of juice)

• Initially the sugarcane waste must be treated with NaOH for improve the absorbency.

• After the caustic treatment it is made neutral then used as adsorbent.

• It use to absorb all kind of water soluble dyes with certain limits.

• Limitation it is not performed for flowing water it required still water.

• The sample can be used once or for limited no of lot.

Peat

• The cellular structure of peat makes it an ideal choice as an adsorbent It has the ability to adsorb transition metals and polar organic compounds from dye containing effluents.

• Peat requires no activation, unlike activated carbon, and also costs much less.

• It has a much larger surface area and hence has better Capacity.

Ash and coal

• An ash concentration increases the adsorption rate of the mixture due to increasing the surface area available for adsorption.

• This mixture can be taken as substitute for activated carbon.

• This shows comparatively lower absorbency.

Silica gel

• An effective material for removing basic dyes, although side reaction such as air binding and air-fouling with particulate matter, prevents it being used commercially.

• Generally it is use for adsorbing the atmospheric moisture and by using similar concept it is used for adsorbent of dye from the waste water.

Decolourisation by use of certain chemicals whereas by use of microorganisms, it is briefly derive below

Chemical treatment for removal of colour from effluent and it is simply done by destroying chromophoric group which are responsible for colour.

The basic process are as below:

1. Ozonation

• It is a very good oxidizing agent due to its high instability compared to chlorine.

• Oxidation by ozone is capable of degrading chlorinated hydrocarbons, phenols, pesticides, and aromatic hydrocarbons.

• Ozonation leaves the effluent with no color and low COD suitable for discharge into environmental waterways.

2. Photochemical method

• Here decolourasition occurs due to high concentration of hydroxyl radicals.

• Here the water by UV treatment in the presence of hydrogen peroxide.

• UV light may be used to activate chemicals such as hydrogen peroxide and the rate of

• dye removal is influenced by the intensity of the UV radiation, pH, dye structure.

3. Oxidative process

• The main oxidizing agent is usually hydrogen peroxide.

• These agents need to be activated by some means, for example ultraviolet light.

• Common oxidizing agents are oxygen, chlorine, sodium hypochlorite, calcium hypochlorite, potassium permanganate, hydrogen peroxide.

• Chemical oxidation removes the dye from dye containing effluent by oxidation resulting in aromatic ring cleavage of the dye molecule Oxidants are used in wastewater treatment.

As per the decolourisation by biological process

This decolourisation occur by the microorganisms which are as follow:-

1. Bacteria

• Many type of bacteria are capable of dye decolourisation.

• Bacterial cultures are capable of degrading azo dyes much bacteria include bacillus subtilis, bacillus cereus.

• It require more time and it is difficult to perform

• Bacteria have a capacity to mineralizing sulfonated azo-mordant yellow.

• An anaerobic to aerobic reaction is required in dye degradation

2. Algae

• Algae species utilize azo dyes as their sole source of carbon and nitrogen.

• Algae are capable of degrading their aromatic amines through azoreductase.

• Algae can be used for stabilization of ponds as they play a role in aromatic amine removal. Where Chlorella and oscillatoria are few important species of algae.

3. Yeast

• Yeasts can adapt and grow in various extreme conditions of pH, temperature and availability of nutrients as well as high concentrations of pollutant.

• The yeast strain possessed the most pronounced ability to remove the dye from solution.

• Yeast (klyveromyces marxianus) are capable of decolourizing ramazol black by 78 – 98%.

Conclusion

There are various technique which can be practice for removal of colour which get remain or unexhausted in waste water in effluent. Physical and chemical method is suitable for dye removal are efficiently results when there is small volume of effluent required to be treated.

Whereas biological process for removal of colour from water is also suitable but for fermentation it require time period. Thus by this it has to be concluded that for decolourisation cannot be practice for flowing water it required stable water for a time period.